BAGHDAD (AP) — An apparently coordinated wave of bombings targeting Shiite Muslims killed at least 78 people in Iraq on Thursday, the second large-scale assault by militants since U.S. forces pulled out last month.

The attacks, which bore the hallmarks of Sunni insurgents, come ahead of a Shiite holy day that draws hundreds of thousands of pilgrims from across Iraq, raising fears of a deepening of sectarian bloodshed. Rifts along the country’s Sunni-Shiite faultline just a few years ago pushed Iraq to the brink of civil war.

The bombings in Baghdad and outside the southern city of Nasiriyah appeared to be the deadliest in Iraq in more than a year.

Thursday’s blasts occurred at a particularly unstable time for Iraq’s fledgling democracy. A broad-based unity government designed to include the country’s main factions is mired in a political crisis pitting politicians from the Shiite majority now in power against the Sunni minority, which reigned supreme under the dictatorship of Saddam Hussein.

Some Iraqis blame that political discord for the lethal strikes.

“We hold the government responsible for these attacks. They (the politicians) are bickering over their seats and these poor people are killed in these blasts,” said Baghdad resident Ali Qassim not long after the first bomb went off.

The attacks began during Baghdad’s morning rush hour when explosions struck the capital’s largest Shiite neighborhood of Sadr City and another district that contains a Shiite shrine, killing at least 30 people, according to police.

Several hours later, a suicide attack hit pilgrims heading to the Shiite holy city of Karbala, killing 48, police said. The explosions took place near Nasiriyah, about 200 miles southeast of Baghdad.

Hospital officials confirmed the causalities. Authorities spoke on condition of anonymity because they weren’t authorized to release figures of the dead and wounded, who numbered more than 100.

The blasts occurred in the run-up to Arbaeen, a holy day that marks the end of 40 days of mourning following the anniversary of the death of Imam Hussein, a revered Shiite figure. During this time, Shiite pilgrims — many on foot — make their way across Iraq to Karbala, south of Baghdad.

Baghdad military spokesman Maj. Gen. Qassim al-Moussawi said the aim of the attacks is “to create turmoil among the Iraqi people.” He said it was too early to say who was behind the bombings.

Coordinated attacks aimed at Shiites are a tactic frequently used by Sunni insurgents.

The last U.S. combat troops left Iraq on Dec. 18, ending a nearly nine-year war. Many Iraqis worry that a resurgence of Sunni and Shiite militancy could follow the Americans’ withdrawal. In 2006, a Sunni attack on a Shiite shrine triggered a wave of sectarian violence that pushed the country to the brink of civil war.

“People have real fears that the cycle of violence might be revived in this country,” said Tariq Annad, a 52-year-old government employee in Sadr City, after Thursday’s bombings.

Attacks on Wednesday targeted the homes of police officers and a member of a government-allied militia. Those strikes, in the cities of Baqouba and Abu Ghraib outside Baghdad, killed four people, including two children, officials said.

Two weeks earlier, militants killed at least 69 people as a wave of bombs ripped through mostly Shiite neighborhoods in Baghdad. An al-Qaida front group in Iraq claimed responsibility.

Iraq’s political mess is providing further ammunition for extremists.

Shiite Prime Minister Nouri al-Maliki’s government issued an arrest warrant for the country’s top Sunni politician last month. The Sunni official, Vice President Tariq al-Hashemi, is holed up in Iraq’s semiautonomous Kurdish region in the north — effectively out of reach of state security forces.

Al-Maliki’s main political rival, the Sunni-backed Iraqiya bloc, is boycotting parliament sessions and Cabinet meetings to protest what its members say are efforts by the government to consolidate power.

Gala Riani, a Middle East analyst at IHS Global Insight, said the political storm feeds into Sunni fears they could be marginalized by the Shiite-dominated government — worries that Sunni militants are trying to exploit.

“The political crisis has set up a perfect scenario for Sunni militants to re-establish themselves,” she said. “It’s very sectarian in nature and gives them fuel for their fire.”

While the political showdown appears far from being resolved, there are tentative signs of progress.

Al-Maliki met Thursday with the Sunni speaker of parliament, Osama al-Nujaifi, a member of al-Hashemi’s Iraqiya party. In televised comments afterward, they described the talks as positive and said they will work to find a way out of the crisis.

Earlier, both men condemned Thursday’s bombings.

In Washington, State Department spokeswoman Victoria Nuland also denounced the “terrorist violence” in Iraq and called the attacks “desperate attempts by the same kind of folk who’ve been active in Iraq trying to turn back the clock.”

Britain’s Foreign Office minister for the Middle East and North Africa, Alistair Burt, urged Iraq’s leaders to renew their efforts to break the political impasse.

Meanwhile, six Iraqiya lawmakers broke ranks with their party over the boycott by attending a parliament session. Ahmed al-Jubouri, one of the Iraqiya lawmakers who participated, said he did so to “encourage all blocs to sit together and open dialogue.”